I've never had a Siamese, but I have had a half-Siamese and my friends have had several Siamese cats.
These are my own personal experiences, and may not be true for everyone.
I'll start with a warning about them.
Have you heard their cries? Seriously, if you haven't, find a video and listen to it. They are VERY loud, VERY vocal, VERY involved in family life, and they will talk and talk and talk and talk......if you cannot bear the sound they make, then don't even think about it. I'm sure somewhere, there is a quiet Siamese, but I've yet to meet one. It's like being haunted. They will cry when they're bored. They will cry when they're alone. They will cry when they're hungry. They will cry when you're right beside them and they just want attention. They will cry when the leave the room. They will cry when the enter the room. They will cry when you say their name (this is cute though). They love the sound of their own voice, and if you don't love it too, you'll cry yourself.
On the plus side, they're incredibly intelligent, love being the centre of family life, are sociable, if a little highly strung, friendly and very loving and affectionate.
They're also easily bored, and when bored, they become destructive. Their intelligence means they can open cupboards and doors (even childproof locks have proved to be no obstacle), and they need a LOT of attention if they're not to investigate, thoroughly, every single corner and tiny space in your home. You'll find them in the attic. They'll be down on the floor behind a heavy cupboard, having slid down to "take a peek" and been unable to get themselves back out again. Four hours later, once you've removed the contents of the cupboard and moved it out, they'll saunter out and demand food. Next day they will do the exact same thing again, and will continue to do so until you build a wall of books across the gap at the top to stop them dropping down.
My attic had two rooms, one fully lined and the other unlined, so I wouldn't let my boy into the unlined room as he'd have disappeared into the eaves and I'd never have seen him again. I shut him in the lined room as he insisted on coming up with me. He climbed out of the window (stupidly, I left it open an inch and he hauled it open further) and scrabbled his way across a pitched slate roof to look into the window of the other room to see what I was up to. That's how nosy he was. I had to squeeze open the other window and grab him before he fell three storeys.
If you're not prepared for them to be potential handfuls, go for a moggy. Seriously, I aged about 20 years over the roof incident.